The invention generally relates to machines for processing diverse documents. In document processing machines, such as mail processing machines, the documents are often stored in document feeders in the form of a stack of documents.
The documents are extracted one by one from the stack and transferred in the downstream direction to undergo specific processing. For example, a feeder can contain a stack of filled envelopes from which the bottom envelope is extracted and is then transferred to a station situated downstream of the machine for moistening the envelope and sealing it. The envelope sealed in this way is then transferred to a downstream franking station. There is represented in FIG. 1a a stack 10 of documents such as envelopes resting on a support 12. The support comprises a horizontal table 14 with apertures through which pass partially rollers 16, 18, 20 mounted to rotate about a horizontal axis 22. A vertical wall 24 connected to the table 14 locates the stacked documents and therefore keeps them stacked.
When the stacked documents are envelopes, the flap of each envelope is folded and these flaps are on the same side as the vertical wall 24, which increases the thickness of the envelope on the same side as the vertical wall 24 and causes the stack to lean as represented in FIG. 1a. As and when envelopes at the bottom of the stack 10 are extracted therefrom by the rollers 16, 18, 20 to be processed downstream of the feeder (in the background in the figures), the stack moves away from the wall 24 (FIGS. 1b and 1c).
This displacement of the stack is also caused by vibrations generated by the envelope extraction mechanism and, more generally, by the various operations that are carried out downstream. If a number of envelopes have been pulled out in succession, the stack 10 is greatly offset in a direction away from the wall 24 (FIG. 1c). It will be noted that the means for extracting an envelope offset in this way, which are situated in the background in FIG. 1c (not shown), can prove of lower performance. Some means can even, in some cases, be unable to extract the envelope offset in this way.
When the offset envelope has been extracted after all and reaches the next processing station downstream of the feeder, it is however not correctly located at the station (misalignment compared to the normal path of the envelopes). Manual intervention by an operator is then necessary to return the envelope to a correct position at the entry of the station in order for it to be processed correctly at this station. The operator must also reposition the stack 10 against the wall 24 of the feeder.
The problems described hereinabove are also encountered with other types of stacked documents such as sheets of paper. However, these problems are exacerbated with envelopes because of the folded flap that makes them thicker and causes tilting of the stack before any envelopes are extracted.